NMR Spectrum Predictor | 1H and 13C NMR Chemical Shift Calculator

Nuclear Magnetic Resonance (NMR) spectroscopy is an analytical technique used to determine the structure of organic compounds by measuring the interaction between nuclear spins and an external magnetic field. The two most common NMR experiments are:

• 1H NMR (proton NMR) - Analyzes hydrogen atoms in a molecule
• 13C NMR (carbon NMR) - Analyzes carbon atoms in a molecule

NMR spectroscopy is critically important in organic chemistry, biochemistry, and pharmaceutical research because it enables scientists to:

• Determine molecular structures
• Confirm the identity of synthetic compounds
• Analyze the purity of samples
• Study molecular dynamics and interactions
• Monitor chemical reactions
• Identify unknown compounds

It's often called the "gold standard" for structure elucidation because it provides detailed information about molecular connectivity and spatial arrangements.

This NMR prediction tool uses empirical methods based on chemical environment analysis and reference data to provide reasonable estimates of chemical shifts. While it can't match the accuracy of high-end commercial NMR prediction software or experimental data, it's quite useful for:

• Educational purposes - Understanding how structure relates to NMR spectra
• Quick preliminary analysis - Getting a first approximation of expected NMR signals
• Structural verification - Confirming basic structural features

For typical organic molecules, you can expect chemical shift predictions within approximately ±0.3 ppm for 1H NMR and ±3-5 ppm for 13C NMR. The accuracy is generally better for common functional groups and standard structural motifs, while predictions for unusual or complex structures may be less reliable.

For research-grade predictions, quantum mechanical methods or more sophisticated database approaches would be recommended, but this tool provides a good starting point for understanding the expected spectral patterns.

Interpreting 1H NMR spectra involves analyzing several key features:

1. Chemical shift (δ, ppm) - Indicates the chemical environment of each hydrogen
2. 0-1.5 ppm: Alkyl hydrogens (CH3, CH2, CH)
3. 1.5-3.0 ppm: Hydrogens adjacent to functional groups
4. 3.0-4.5 ppm: Hydrogens attached to electronegative atoms (O, N)
5. 5.0-6.5 ppm: Vinylic hydrogens (C=C-H)
6. 6.5-8.0 ppm: Aromatic hydrogens
7. 9.0-10.0 ppm: Aldehyde hydrogens (CHO)
8. 10.0-13.0 ppm: Carboxylic acid hydrogens (COOH)

1. Integration - The relative area under each peak, indicating the number of hydrogens

1. Multiplicity - The splitting pattern of peaks:
2. Singlet (s): No adjacent hydrogens
3. Doublet (d): One adjacent hydrogen
4. Triplet (t): Two adjacent hydrogens
5. Quartet (q): Three adjacent hydrogens
6. Multiplet (m): Complex pattern from multiple interactions

1. Coupling constants (J, Hz) - Measure the magnetic interaction between hydrogens

By analyzing these features, you can deduce structural information about the molecule, identify functional groups, and confirm chemical connectivity.

13C NMR interpretation focuses primarily on chemical shifts, which provide information about carbon environments:

1. Chemical shift ranges (δ, ppm):
2. 0-30 ppm: Alkyl carbons (CH3, CH2, CH)
3. 30-50 ppm: Carbons adjacent to functional groups
4. 50-90 ppm: Carbons attached to heteroatoms (O, N)
5. 110-150 ppm: Aromatic and unsaturated carbons (C=C)
6. 160-185 ppm: Carbonyl carbons (C=O)
7. 185-220 ppm: Aldehyde and ketone carbons

1. DEPT experiments distinguish between different carbon types:
2. DEPT-45: All CH, CH2, and CH3 give positive signals
3. DEPT-90: Only CH gives signals
4. DEPT-135: CH and CH3 give positive signals, CH2 gives negative signals
5. Quaternary carbons (no attached H) don't appear in DEPT

1. Signal intensity is not directly proportional to the number of carbons (unlike 1H NMR)

1. Coupling is usually not observed in routine 13C NMR due to decoupling techniques

13C NMR is particularly valuable for identifying the carbon skeleton of a molecule, confirming the presence of specific functional groups, and distinguishing between isomers that might have similar 1H NMR spectra.

NMR prediction serves several important practical purposes in chemistry:

• Synthetic planning - Predicting the NMR spectrum of a target molecule before synthesis
• Structure verification - Comparing experimental spectra with predicted spectra to confirm product identity
• Education - Teaching students the relationship between molecular structure and spectroscopic properties
• Peak assignment - Aiding in the assignment of complex experimental spectra
• Structure elucidation - Narrowing down possible structures for unknown compounds
• Publication preparation - Helping to assign and report spectral data in scientific publications

In research settings, chemists often use NMR prediction tools when designing new synthetic routes, to anticipate what spectral features would confirm successful reactions. In the pharmaceutical industry, these tools help with quality control, ensuring that manufactured compounds match their expected spectral profiles.

SMILES (Simplified Molecular Input Line Entry System) is a line notation for describing chemical structures using ASCII strings. It's a concise way to represent molecular structures in text format. Some basic rules for writing SMILES include:

• Atoms are represented by their atomic symbols (C, N, O, etc.)
• Uppercase letters represent aliphatic atoms (C, N, O)
• Lowercase letters represent aromatic atoms (c, n, o)
• Single bonds are implied between adjacent atoms
• Double bonds are represented by '='
• Triple bonds are represented by '#'
• Branching is indicated by parentheses

Common examples of SMILES notation:

• CCO - Ethanol (CH3CH2OH)
• CC(=O)O - Acetic acid (CH3COOH)
• c1ccccc1 - Benzene
• CC(C)=O - Acetone ((CH3)2CO)
• C1CCCCC1 - Cyclohexane

To use SMILES in this tool, simply enter the SMILES string for your molecule in the input field and click 'Predict'. You can also click one of the example molecules to see how the tool works.